The following report was received from the Commonwealth of Pennsylvania via email and facsimile:

"Event Type: Loss of licensed material in a quantity greater than or equal to 1000 times the Appendix C quantities in part 20.

"Notifications: NRG Energy discovered the event on March 7, 2016, [at their Seward, PA location,] and submitted a report to the Department [Pennsylvania Department of Environmental Protection] on March 9, 2016. This event is reportable as per 10 CFR 20.2201(a)(1)(i).

"Event Description: On Monday March 7, 2016, while conducting the six month inventory check of the radioactive sources at the Seward Power Plant, one tritium exit sign was found missing. The exit sign was installed above a door located in Seward's Fuel Barn. The last inventory check was conducted September 11, 2015, and the exit sign was present at that time. The exit sign was manufactured by EMERG-LITE and was an Everlite series sign. The sign contained between 9.5 - 11.5 Ci of tritium gas at the time of manufacture and was to be replaced before February 2023. The sign was last known to be in good condition and not damaged. No cause for the missing sign has been identified and no exposures have been recorded at this time.

"Cause of the Event: Unknown at this time. The plant is currently searching the site and conducting interviews with personnel.

"Actions: The Department will be following up with the facility for any additional information. The plant is also conducting refresher radiation training to plant personnel. More information will be provided upon receipt."

Pennsylvania Event Report ID No: PA160009.

THIS MATERIAL EVENT CONTAINS A "LESS THAN CAT 3" LEVEL OF RADIOACTIVE MATERIAL

Sources that are "Less than IAEA Category 3 sources," are either sources that are very unlikely to cause permanent injury to individuals or contain a very small amount of radioactive material that would not cause any permanent injury. Some of these sources, such as moisture density gauges or thickness gauges that are Category 4, the amount of unshielded radioactive material, if not safely managed or securely protected, could possibly - although it is unlikely - temporarily injure someone who handled it or were otherwise in contact with it, or who were close to it for a period of many weeks. For additional information go to http://www-pub.iaea.org/MTCD/publications/PDF/Pub1227_web.pdf

The licensee reported that a Siemens C-200 Gauge, model L 640 containing a Ra-226 0.005 Ci source, was run over by a pick up truck and damaged. Damage to the gauge was limited to the electronics package and battery. The source remains properly contained and un-damaged. A survey of the area indicates no leakage and no exposures to personnel. The gauge has been placed in a secure location and will be sent back to the manufacturer for repairs.

"What Happened: One (1) each Isotope Product Laboratory, 12.8 nCi Am-241 check source, RP# 0895 was to be shipped, along with three other sources, to Nellis AFB in support of USAFSAM/OEC personnel. The PRSO [Permit Radiation Safety Officer] could not immediately locate RP# 0895.

"The PRSO checked the RAM [Radioactive Material] sign-out log to determine if the source had been signed out to other OE personnel. The log did not show evidence of the source having been signed out. The PRSO questioned Radioanalytical Lab, Dosimetry Lab, Calibration Lab, AFRAT, Consulting and Education personnel to determine if anyone was using the source. All of them had a negative reply. All laboratories were thoroughly searched as were the OEC equipment cases used in the Nellis operations. AFRAT equipment cases in WRM were also searched. The source was not located.

"The PRSO determined the source had last been accounted for during the RAM inventory dated 17 August 2015. Additional investigation revealed that the prior PRSO had been requested to send the source, along with two other sources, to Nellis AFB in support of OEC personnel in September 2015. These sources were never signed out of the inventory when sent to Nellis AFB. Additionally, no OEC personnel recall using the source during that period. The other two sources requested were received back at USAFSAM on 5 October 2015. DOE personnel working with OEC personnel at Nellis AFB, as well as the Nellis IRSO [Installation Radiation Safety Officer], were contacted to see if they had the source in their possession. All had a negative reply. It cannot be determined if the source was lost at USAFSAM or Nellis AFB.

The PRSO contacted the IRSO, at 1531, 17 February 2016 to inform him of the potential lost source.

THIS MATERIAL EVENT CONTAINS A "LESS THAN CAT 3" LEVEL OF RADIOACTIVE MATERIAL

Sources that are "Less than IAEA Category 3 sources," are either sources that are very unlikely to cause permanent injury to individuals or contain a very small amount of radioactive material that would not cause any permanent injury. Some of these sources, such as moisture density gauges or thickness gauges that are Category 4, the amount of unshielded radioactive material, if not safely managed or securely protected, could possibly - although it is unlikely - temporarily injure someone who handled it or were otherwise in contact with it, or who were close to it for a period of many weeks. For additional information go to http://www-pub.iaea.org/MTCD/publications/PDF/Pub1227_web.pdf

"On March 17, 2016, at 0115 [EDT], Watts Bar Unit 1 (WBN1) entered Technical Specification Limiting Condition of Operation (TS LCO) 3.0.3 due to the inoperability of both trains of the Emergency Gas Treatment System (EGTS). TS LCO 3.7.12 Condition B was also entered at this time due to the inoperability of both trains of the Auxiliary Gas Treatment System (ABGTS). The train B EGTS and train B ABGTS had been removed from service for scheduled maintenance, when at 0115, the train A Auxiliary Air Compressor became inoperable. On March 17, 2016, at 0133, the train A Auxiliary Air Compressor was declared OPERABLE, and TS LCO 3.0.3 and 3.7.12 Condition B were exited.

"The auxiliary air system supports the EGTS by providing a safety grade air supply. When train A auxiliary air became inoperable, the supported train A EGTS and ABGTS became inoperable, creating a condition where both trains of EGTS and ABGTS were unavailable. In the event of an accident, the EGTS establishes a negative pressure in the annulus between the shield building and the steel containment vessel and the ABGTS establishes a negative pressure in the Auxiliary Building Secondary Containment Enclosure (ABSCE). Filters in these system mitigate the release of radioactive contaminants to the environment.

"WBN1 remained in Mode 1 at 100% power and no safety functions were required during the event.

"This event is reportable under 10 CFR 50.72(b)(3)(v)(C) and (D) as a condition that could have prevented the fulfillment of a safety function.

VALID ENGINEERED SAFETY FEATURE SYSTEM ACTUATION DUE TO LIGHTNING STRIKE

"At 1515 [CDT] on March 17th 2016, Grand Gulf Nuclear Station received a valid actuation signal of the Division 2 Engineered Safety Feature (ESF) Load Shedding and Sequencing system. The actuation signal was most likely caused by a lightning strike to the offsite power source supplying this ESF bus. This caused a loss of the in service shutdown cooling system and associated system actuations.

"Grand Gulf Nuclear Station (GGNS) was in Mode 5 at 85 [degrees] F coolant temperature. Reactor Cavity was flooded to High Water Level with a time to reach 200 [degrees] F of 7.5hrs. GGNS is conducting a planned refuel outage with core alterations in progress. Systems were aligned as follows:

"Division 2 Diesel Generator was OPERABLE and the associated ESF bus aligned to transformer ESF12 (115KV Port Gibson offsite feeder). Residual Heat Removal (RHR) system 'B' was in service in shutdown cooling being supplied from this ESF bus (16AB) with Alternate Decay Heat Removal available as a backup.

"Division 3 Diesel Generator was unavailable due to planned maintenance on support systems. The associated ESF bus was also aligned to transformer ESF12 (115KV Port Gibson offsite feeder).

"Division 1 Diesel Generator was available and the associated ESF bus aligned to the transformer ESF 11 (Switchyard offsite power feeders Baxter-Wilson and Franklin). Power was never lost to this bus. RHR 'A' and Low Pressure Core Spray (LPCS) were not available due to planned maintenance (tagged out of service).

"ESF 21 Transformer was out of service for planned maintenance.

"A suspected lightning strike caused a momentary perturbation in power in the 115KV Port Gibson line causing the Division 2 Load Shedding and Sequencing (LSS) system to actuate. This actuation caused a loss of Residual Heat Removal system 'B' due to being shed (expected). The Division 2 Diesel Generator started and tied onto the bus as expected, restoring power in 7 seconds. Shutdown cooling was restored at 1518 [CDT] and was out of service for 3 mins 13 sec. Reactor coolant and spent fuel pool temperatures remained at 85 [degrees] F throughout this scenario. Core Alterations were suspended and fuel placed in its designated location per the approved movement plan. Division 3 systems; High Pressure Core Spray, Standby Service Water System 'C', and Division 3 Diesel Generator were tagged out of service for planned maintenance. Division 3 Diesel Generator received a valid actuation signal but did not start due to being out of service. The Division 3 bus was restored manually to ESF 11.

"All safety systems operated as expected for the loss of power to ESF 12 and Division 2 LSS actuation.